Look, I'm not saying that Sigma Foveons never alias. There are other things happening to create artifacts that are strictly not aliasing. Without an AA filter, not only can detail from above Nyquist be aliased down, but also detail below Nyquist tends to be greatly boosted. Boosted detail in the range between Nyquist and 1/2 Nyquist often don't "look right" because of the sampling process itself, even though they are perfectly valid (not aliased). In order for those higher details to look right, it's necessary to invoke the part of the sampling theorem that is usually ignored with images: reconstruction. The zooming examples I gave are a way to "reconstruct" those higher details below Nyquiest.

I'm not a Foveon advocate, but I think they get a bad rap because anything that doesn't look right is blamed on the lack of AA filter.